Counter-current flow limitation at lower ends of vertical pipes

Experiments on counter-current flow limitation (CCFL) in a vertical pipe with a round upper end and a sharp lower end are carried out to understand flow patterns under CCFL conditions and to investigate effects of pipe length and water level in an upper tank on CCFL characteristics. As a result, the following conclusions are obtained: (1) CCFL occurs at the lower end of the vertical pipe when the pipe length is more than 10 times as large as the pipe diameter, D, and the water level in the upper tank is more than 15 times as large as D. (2) CCFL data measured by Bharathan et al. and the correlation proposed by Zapke and Kroger agree rather well with the present data within their experimental ranges. (3) When CCFL occurs at the lower end of the pipe, CCFL characteristics do not depend on pipe length and water level in the upper tank. (author)